To our knowledge, this is the first prospective series describing the use of lung ultrasound in children as a potential real-time diagnostic triage tool during a mass casualty-type incident due to an acute respiratory illness pandemic surge [17, 18]. Testa et al. have reported on similar lung ultrasound findings in adults during the 2009 H1N1 influenza A pandemic . Single case reports of clinician-performed lung ultrasound to monitor the progression of H1N1 influenza-associated ARDS  and point-of-care echocardiography to diagnose H1N1 influenza myocarditis  have been described. Retrospective reports of the role of ultrasound in mass casualty incidents during disasters such as earthquakes have also been described [21, 22]. Lichtenstein et al. described an algorithm using lung ultrasonography to distinguish between various respiratory pathologies of the lung . We modified Lichtenstein’s BLUE protocol  to recognize basic lung ultrasound patterns to distinguish between the normal unaffected lung, viral pneumonia pattern, and bacterial pneumonia (Figure 3). Scanning the posterior thorax was added to increase the sensitivity of the protocol . Point-of-care lung ultrasound was able to identify, in real-time, four groups of pandemic patients: viral pneumonia only (subpleural consolidations and/or B-lines or confluent B-lines), bacterial pneumonia only (lung consolidation with sonographic air bronchograms), both viral and bacterial pneumonia (Figure 7), and normal lungs (A-lines only). Our calculated Kappa was 0.82, which means that the interobserver agreement in distinguishing between these ultrasound findings was excellent.
These ultrasound findings facilitated triage and immediate decision making regarding the need for respiratory isolation in a negative pressure room without waiting for chest X-ray. Our median time to chest X-ray tripled (Table 1) during the pandemic compared to a time period prior to the pandemic. Our time to chest X-ray interpretation during the pandemic was longer than the median of 98 min reported by Zanobetti et al. in the study of emergency department lung ultrasound in non-pandemic conditions .
When lung consolidation with sonographic air bronchograms was visualized, point-of-care ultrasound facilitated the immediate decision to treat with antibiotics, without waiting for chest X-ray. Visualization of viral pneumonia on ultrasound may be useful to assist in the decision to initiate immediate empiric treatment with antiviral medication for future pandemic or epidemic influenza patients. In a large cohort of hospitalized H1N1 influenza A pandemic patients, only 73% of patients with radiographic evidence of pneumonia received antiviral drugs, whereas 97% received antibiotics . Better recognition of viral pneumonia by ultrasound may impact outcomes, as available data have shown treatment with antiviral medication reduces mortality in hospitalized patients with influenza, even when therapy is initiated after 48 h of illness onset .
Our sample size was limited by the inability to enroll during the surge of pandemic patients due to time and resource constraints. Selection bias from convenience sampling may have occurred because patients were more likely to have been enrolled at less busier or better staffed times. In general, the patients in this series had illnesses severe enough to warrant investigation with chest X-ray. Thus, information about less ill or asymptomatic pandemic patients is lacking.
Although our calculated interobserver agreement for lung ultrasound to distinguish between viral and bacterial pneumonia is high, the number of total observations was limited, and this is reflected in our wide 95% confidence intervals. However, it is notable that our point estimate Kappa for ultrasound is higher than the reported interobserver agreement for chest X-ray for pneumonia by pediatric radiologists, 0.51 (0.39 to 0.64) .
Due to the large numbers of patients presenting to our emergency department during the pandemic, only hospitalized patients (four patients in our series) were confirmed with 2009 H1N1 influenza A . Finding small subpleural consolidations and/or B-lines on ultrasound allows the recognition of viral pneumonia from bacterial pneumonia (lung consolidation with sonographic air bronchograms), but it is unknown if different viruses have unique lung ultrasound patterns (e.g., influenza A from RSV). We could not report test performance characteristics, such as sensitivity and specificity, as there was no practical reference gold standard for viral pneumonia at the time our study was conducted. Additionally, chest X-ray cannot be used as a gold standard for viral pneumonia. However, according to the New York City Department of Health, >90% of the circulating virus during this pandemic time period was the novel influenza A H1N1 .